1. Field of the Invention
The present invention relates to a disarm circuit using a semiconductor switch device, particularly relates to a disarm circuit using a semiconductor switch device used for an electrotherapy apparatus for defibrillation.
2. Related Art
An arrhythmia, particularly ventricular fibrillation in the heart of a patient having cardiac disease suddenly kills the patient. To terminate the fibrillation, an electrotherapy apparatus for terminating the fibrillation by applying a shock by an electric pulse to the heart of the patient (also called a defibrillator) is generally used.
Such an electrotherapy apparatus is provided with an electric energy storage section that generates a high-voltage electric pulse such as a capacitor. A method of forcedly discharging high-voltage electric energy left inside the electrotherapy apparatus (the electric energy storage section) after the electrotherapy apparatus is used to secure safety has been considered.
For one method, there is a method of providing a disarm circuit using a semiconductor switch device.
Referring to the drawings, a method of discharging by a disarm circuit using a semiconductor switch in a conventional type electrotherapy apparatus will be described below.
FIG. 7 is a schematic drawing for explaining a method of disarming by the disarm circuit using the semiconductor switch in the conventional type electrotherapy apparatus.
As shown in FIG. 7, the on-off control of the semiconductor switch 201 is performed by a semiconductor switch driving section 203 controlled according to a control signal 206 from a microprocessor 202.
A resistor for disarming 205 is inserted between an electric energy storage section (a capacitor) 204 for storing high-voltage electric energy and the semiconductor switch 201, current flows to a ground terminal 208 via the resistor for disarming 205 by turning on the semiconductor switch 201 and electric energy is disarmed.
However, the method of discharging by the disarm circuit using the semiconductor switch in the conventional type electrotherapy apparatus has the following problems.
The semiconductor switch 201 is controlled by the semiconductor switch driving section 203 controlled according to a control signal from the microprocessor 202 and therefore, when the control of the semiconductor switch 201 is disabled due to the unexpected cutoff of power supply by the disconnection of a battery and others and some failure of the apparatus such as the single fault of a control circuit, the semiconductor switch 201 is turned off and energy stored in the electric energy storage section 204 is not disarmed.
Therefore, the method of disarming by the disarm circuit using the semiconductor switch in the conventional type electrotherapy apparatus has a problem of safety that in case the control of the switch is disabled because of some cause, high-voltage electric energy remains in the circuit undischarged and when the electrotherapy apparatus is operated or repaired, an operator or a repairman may get electric shock.
The invention is made to solve the problem of the related art and the object is to provide a disarm circuit using a semiconductor switch device wherein the safety of an electrotherapy apparatus can be secured by disarming even if the control of a semiconductor switch is disabled because of some cause.
To achieve the object, a disarm circuit using a semiconductor switch device according to a first aspect is based upon A disarm circuit comprising a semiconductor switch device discharging electric energy stored in an electric energy storage section by turning on the semiconductor switch device according to a control signal from a control circuit via a first resistor for disarming provided between one terminal of the electric energy storage section and a first terminal of the semiconductor switch device; and
a second resistor for limiting current which flows from one terminal of the electric energy storage section and for transmitting the current to a control terminal of the semiconductor switch device, the second resistor being provided between one terminal of the electric energy storage section and the control terminal of the semiconductor switch device, electric energy stored in the electric energy storage section automatically turns on the semiconductor switch device and is discharged via the resistor for disarming in case the control of the semiconductor switch is disabled because of some cause when the electric energy storage section is disarmed.
As a disarm circuit using a semiconductor switch device according to a second aspect is formed so that a transformer is at least provided, a primary side area controlling current on the primary side of the transformer according to a control signal for controlling the semiconductor switch device, the primary area being provided on the primary side of the transformer;
a secondary side area directly driving the semiconductor switch device, the secondary side area being provided on the secondary side of the transformer,
wherein the primary side area receives a control signal, transmits power for controlling the semiconductor switch device to the secondary side area and inhibits back electromotive force caused when current that flows on a primary winding of the transformer is cut off, back electromotive force caused when current flowing in the transformer is cut off is inhibited.
As the secondary side area in a disarm circuit using a semiconductor switch device according to a third aspect is formed so that the secondary side area receives power supplied from the primary side area, transmits power for controlling the semiconductor switch device to the semiconductor switch and cuts off voltage caused by back electromotive force caused when current that flows on a primary winding of the transformer is cut off so that impedance is lower, compared with the second resistor, the control according to a control signal of the semiconductor switch device is also preceded in a state in which electric energy is stored in an electric energy storage section.
As in the secondary side area in a disarm circuit using a semiconductor switch device according to a fourth aspect, a terminal at one end of a secondary winding of the transformer is connected to a first Zener diode, a second Zener diode such that the same kind terminals of the first and second Zener diodes are connected with the same terminals face to face is connected to a control terminal of the semiconductor switch device via a resistor, a terminal at the other end of the secondary winding of the transformer is connected to a second terminal of the semiconductor switch device and a capacitor is connected between the second Zener diode and the second terminal of the semiconductor switch device, the secondary side area receives power supplied from the primary side area and transmits power for control to the semiconductor switch device.
As in a disarm circuit according to a fifth aspect the plural semiconductor switch devices are provided, the withstand voltage against the application of high voltage has a value acquired by adding the withstand voltage of the switch device of each stage.
As in a disarm circuit according to a sixth aspect, each second resistor for limiting current is connected between one terminal of the electric energy storage section and the control terminal of each semiconductor switch device.
As in a disarm circuit according to a seventh aspect, each third resistor for equalizing the characteristic of each semiconductor switch devices is connected between a first terminal and a second terminal of each semiconductor switch device.
As in a disarm circuit according to an eighth aspect, the second resistor for limiting current for a first stage is connected between one terminal of the electric energy storage section and a control terminal of a semiconductor switch device of the first stage and the second resistor for limiting current for a second or the subsequent stage is connected between a second terminal of the semiconductor switch device and a control terminal of a semiconductor switch device of the next stage.
As a disarm circuit using a semiconductor switch device according to a ninth aspect uses an insulated gate bipolar transistor (IGBT) for the semiconductor switch device, the first terminal functions as the collector, the second terminal functions as the emitter, the control terminal functions as the gate and one terminal of the electric energy storage section is a positive terminal, the device (IGBT) having both the low saturation voltage characteristic of a bipolar transistor and the high-speed switching characteristic of a power MOSFET can be used.
As a disarm circuit using a semiconductor switch device according to a tenth aspect uses a N-channel MOSFET for the semiconductor switch device, the first terminal functions as the drain, the second terminal functions as the source, the control terminal functions as the gate and one terminal of the electric energy storage section is a positive terminal, the N-channel MOSFET can be used for the semiconductor switch device.
As a disarm circuit using a semiconductor switch device according to an eleventh aspect uses a P-channel MOSFET for the semiconductor switch device, the first terminal functions as the drain, the second terminal functions as the source, the control terminal functions as the gate and one terminal of the electric energy storage section is a negative terminal, the P-channel MOSFET can be used for the semiconductor switch device.
As an electrotherapy apparatus according to a twelfth aspect is provided with the disarm circuit using the semiconductor switch device according to any of the first to the eleventh aspects, an external discharging circuit that generates electric pulse and outputs electric energy to a living body (a patient), the electric energy storage section and a charging circuit that charges the electric energy storage section, the safety of the electrotherapy apparatus can be secured by disarming even if the control of the semiconductor switch is disabled because of some cause when the electric energy storage section is disarmed.